1. Field of the Invention
The present invention generally relates to a slice image automatic alignment method and apparatus used for comparing a tomographic image of an object such as a computerized tomography (CT) image with another tomographic image of the same object which are taken at different times. The tomographic image is generated by CT, MRI(magnetic resonance imaging) or the like.
2. Description of the Related Art
In a medical field, comparison between a present image and a previous image provides a clue for determining whether a shade in an image is a tumor or not and whether it is malignant or not. As one method for the comparison of images, when a doctor finds a suspicious shade in a diagnostic image, the doctor may search for comparison images showing a position which corresponds to that of the diagnostic image so as to compare the images. The technique for supporting the doctor to compare images is disclosed in, for example, “METHOD FOR AUTOMATICALLY COMPARING SLICED IMAGES OF CHEST THREE-DIMENSIONAL TOMOGRAPHIC IMAGES”, Japanese laid-open patent application No. 10-53172 and “COMPARATIVE INTERPRETATION OF RADIOGRAM BY CT IMAGE FOR MASS EXAMINATION”, Ukai et al., JAMIT Frontier '98, pp140-145.
The above-mentioned technique in “METHOD FOR AUTOMATICALLY COMPARING SLICED IMAGES OF CHEST THREE-DIMENSIONAL TOMOGRAPHIC IMAGES” is a method for comparing each slice of the diagnostic images with comparison image slices for finding a corresponding comparison image. Although the method can cope with changes of body condition and movement of the lower part of a lung for breathing, there is a problem that the process takes a long time since the slice needs to be compared with comparison image slices one by one. According to the above-mentioned conventional technique “COMPARATIVE INTERPRETATION OF RADIOGRAM BY CT IMAGE FOR MASS EXAMINATION”, sections of a lung field are classified, then, features such as a lung field area, a heart area, and a descending aorta are extracted and automatic image comparison is performed on the basis of the location of the features. However, there is a problem that it takes a long time to extract the features.
Accordingly, when a doctor carries out diagnosis by comparing chest tomographic images, it a takes time to see a comparison image which corresponds to the diagnostic image, or it is necessary to compare present images with previous images. In this case, since all images need to be compared, normal images as well as suspicious images need to be compared. Therefore, it takes time to perform often useless comparisons.